High-power resonance absorption isolator having ferrite slab offset from polepieces so as to be non-uniformly magnetized



y 1963 L. A. BLASBERG ETAL 3,099,806

HIGH-POWER RESONANCE ABSORPTION ISOLATOR HAVING FERRITE SLAB OFFSET FROMPOLEPIECES so AS TO BE NONUNIFORMLY MAGNETIZED Original Filed March 15,1956 zimz 5 i I i A Eras.

United States The present invention relates to microwave devices and isa continuation of copending application, Serial No. 572,176, Lawrence A.Blasberg et al., High-Power Resonance Absorption Isolator, filed March15, 1956, now abandoned. More particularly, it relates to anonreciprocal isolator adapted to be used in microwave transmissionmeans to permit the passage of electromagnetic energy therethrough inone direction and to prevent the passage of such energy in the oppositedirection.

In a microwave system it is customary to interconnect the variouscomponents thereof by means of reciprocal transmission means such ashollow waveguides. Due to this reciprocal nature characteristic,electromagnetic energy may be propagated through the transmission meanswith equal facility in either direction. Since the output power, thefrequency, and the frequency stability of a microwave generator arenormally dependent in some degree on the load into which it is working,it is desirable to place a nonrcciprocal isolator in the otherwisereciprocal transmission means. Such an isolator should permit the freepassage of electromagnetic energy propagating in the forward directionbut should completely absorb energy propagating in the reversedirection.

Although isolators of a Wide variety have been provided, one of the mostefiicient types are those employing a gyroresonant or ferrite elementfor absorbing the electromagnetic energy. Such a member isasymmetrically positioned in a section of waveguide so that the plane ofcircular polarization of the electromagnetic energy will passtherethrough. In addition, a biasing magnetic field is created in thegyroresonant or ferrite clement substantially transverse to thedirection of propagation and parallel to the plane of circularpolarization. As a result, electromagnetic energy propagating in onedirection and having a frequency equal to the gyroresonant frequencywill be coupled into the electron spins and absorbed thereby.

Heret-ofore, it has been customary for the biasing flux field within thegyroresonant or ferrite member to be homogeneous or of uniform density.This in turn will insure the gyroresonant frequency being substantiallyuni form in all portions of the gyroresonant or ferrite member. Althoughsuch prior art isolator devices have been effective to absorbelectromagnetic energy traveling in the reverse direction, their abilityto effectively do so is confined to a narrow band of frequenciescentered around the gyroresonant frequency. As the difference betweenthe gyroresonant frequency and the frequency of the electromagneticenergy increases, the amount of isolation rapidly decreases.

It is now proposed to provide a more eificient gyroresonant isolatorwhich will provide :a higher degree of isolation over a wide band offrequencies than has heretofore been possible. More particularly, thisis to be accomplished by providing an isolator in which a gyroresonantor ferrite member is disposed in a waveguide and a heterogeneous fluxfield extends transversely therethrough. Since the flux density of thisfield varies transversely of the gyroresonant or ferrite member, thegyroresonant freatent U Patented July 30, 1963 ice quency inside of themember may be made to vary transversely thereof so as to correspond tothe transverse position of the plane of circular polarization. As aresult, even though the frequency of the electromagnetic energy mayvary, as the plane of circular polarization moves it will always belocated in the portion of the ferrite member where gyroresonance isoccurring. This in turn will insure the isolator providing a high degreeof isolation over a wide band of frequencies.

FIG. 1 is a schematic perspective view of an embodiment of the device ofthe present invention;

FIGS. 2 and 3 are cross-sectional schematic views of the device of FIG.1;

FIG. 4 is a cross-sectional plan View of the device of FIG. 1 withdashed lines representative of the magnetic fieid of a wave beingpropagated from a generator to a load; and

FIG. 5 illustrates the magnetic field distribution in a planetransversely across the waveguide in the device of FIG. 1.

Referring now to the drawings, FIGS. 1, 2 and 3 show an embodiment of anisolator 10 which is adapted to unidirectionally attenuate energyreflected from a load so that it does not return to the microwavegenerator from whence it originated. The isolator 10* comprises asection 12 of conventional rectangular waveguide having flanges 14 and16 to enable it to be inserted in the waveguide interconnecting amicrowave generator with its associated load.

In accordance with a preferred embodiment of the invention, ferriteslabs 1 8 and 20 are disposed contiguous to opposite inner surfaces ofthe respective broad sides of the section 12 of rectangular waveguideintermediate the center lines and corresponding edges thereof. Theferrite slabs 18 and 20* are of the order of 70 mils thick and fromone-fourth to one-half the width of the section 12 of waveguide inwidth. In general, the length of the ferrite slab 22 along thelongitudinal axis of the waveguide is not critical and, for X-band, maybe within the range of from 0.75 to 2.0 inches or longer and the edgesof the slabs may be tapered, as shown, so as to minimize thestanding-wave-ratio resulting from the insertion of the isolator 10 intothe waveguide. Further, any ferrite material which can be made toexhibit gyroresonance throughout the desired band of frequencies withinwhich operation is intended may be employed for the slabs 18, '20. As apractical matter, however, it is desirable to employ ferrite materialswhich have high resistivities so as to the insertion loss in the Wavepropagated in the forward direction. Examples of ferrite materials whichhave been suitable for slabs 18, 20* are ferrites known commercially asGeneral Ceramic R1 or Ferroxcu'be 106.

The apparatus for producing the asymmetrical magnetic field distributionacross the waveguide section 12 includes pole pieces 22, 24 andpermanent magnet 26. The pole pieces 22, 24- extend between the flanges14, 16 and are inserted through apertures in the waveguide section 12which are disposed directly opposite each other in the broad sidesthereof and oriented so as to be parallel to the longitudinal axis ofthe waveguide. Further, the apertures are 0.150 inch wide and disposedalong one side of the waveguide over the edges of ferrite slabs 18, 20nearest the side of the waveguide. The face of each of the pole pieces22, 24 is made flush with the respective inner surface of the broad sideof waveguide section 12. In the present embodiment, the pole pieces 22,24 are made of 0.150 inch thick Armco iron so as to completely fill theapertures through the waveguide, 0.125 inch of the face of each of thepole pieces 22, 24 being covered by the corresponding ferrite slab 20,18, respectively.

The permanent magnet 26 is of the horseshoe type and may, for example,be composed of a magnetic material known commercially as Alnico V. Inorder to achieve the magnetic flux distribution in accordance with thepresent invention, the horseshoe magnet is disposed wave generator tothe load, it is evident that the magnetic field presented to point A isrotating in a clockwise direction with respect to the applied staticmagnetic field, as viewed in the drawing. Electromagnetic energyreflected over the portion of Waveguide including the center lines 5from the load would, therefore, be propagated back toof the broad sidesthereof so that the pole pieces of the wards generator 14 and,accordingly, would present a magnet 26 are contiguous to the pole pieces22, 24 as magnetic field at point A that rotates in thecounterparticularly illustrated in FIG. 2. The magnetic field clockwisedirection with respect to the applied static magdistribution thusproduced is represented by the charnetic field. In accordance with theinvention, the polarity acteristic 30 of FIG. 5. Referring to FIG. 5, apartial of the magnetic field produced by magnet 26 is poled crosssection of the device of FIG. 1 including the ferrite so as to couple tothe aforementioned magnetic field rotatslab 20, pole piece 22, and aportion of the Waveguide ing in the counterclockwise direction. Inaddition to section 12 is shown for the purpose of referencing maghecharacteristics of the ferrite material actually employed, netic fieldintensity versus position across the wavethe frequencies at whichgyroresonance occurs is deterguide, 15 mined by the direct-currentmagnetic field. Inasmuch as In accordance with the present invention,the magnetic the intensity of the magnetic field varies considerablyfield intensity as represented by characteristic must across the ferritslab Z2, attenuation in the backward dipass through or equal thatintensity required to effect reotion is effected over a broad range offrequencies. gyroreso-nance within the ferrite slabs 18, 20 along aRepresentative performance characteristics of an X- plane whe ther is ubtantially pu e circular polariza- 2O band rectangular waveguideresonance absorption isolator tion. Inthe present case, a plane of thistype is located made in accordance with the present invention aretabumidway between the center lines and the respective edges latedbelow:

Waveguide Length of Weight of Ferrite Ferrite Peak Band InsertionIsolation, Back-t0- height, in. device, in. magnet length, in. usedpowers Width, loss, db db front absorpused, oz. used, kw. percent tionratio 0. 500 i 1. 75 I 20 1.6 106 350 15 5.5 220 240 l of the broadsides of the waveguide. The exact location Typical performancecharacteristics of the above-menof: the plane will vary as function'ofthe frequency of the tioned 350 kw. high-power resonance absorptionisolator electromagnetic energy being propagated in the waveover a 10%frequency band in the X band region are: guide (a) A voltage standingwave ratio less than 1.09; In event .Uhalt 1 Slabs arefomPosed of (b) Aninsertion loss of from 0.41 to 0.51 decibels General Ceramic R-l orFerroxcube 106 ferrite matekl-iowatts peak: d n p power inpu an rial,the s t fi Intensity eflect gyroreaonance P ((3) Isolation of from 23 to30 decibels with 30 kilowatts theX band region is of the order of 4000gauss. Also, in I k b 1Q d pea ac. war power.

proceeding toward the center line from the nearest point H h at hi hgymq-esonmce in h f it material is the characteristics of the resonanceabsorption isolator effected, the magnetic field intensity progressivelydecreases have been measured as function of 1lempemtllm fromuntil theintensity at the center line is substantially less R The insertion 1088is decreased 0.3 than that required to produce gyroresonance, F h db andthe isolation 3.5 db in this temperature range. The in the event thatthe ferrite slab should extend across Chang? resonance field Strength ofthe feI'IliTe gecmetfy the center line, the intensity of the magneticfield across 15 F 'p r f by a change in field T ng h f 1116 the-centerline is made less than that required to produce magnetic F withtemperature- This gi a m imum gyroresonance so as not to effectbidirectional attenuaof m with tempfilftltum- This nim m detion.Althou-ghthe permanent magnet 26 has been shown tumng to Similar Gilliet mperatures of the and described in connection with the device of FIG.1, three ferwgmasmti; matem'al's in the magnetic circuit. the use of anelectromagnet to establish a magnetic field Ferroxcwba 105 ferrite Armcoiron and AlHiCO V P rmain accordance with the present invention isconsidered s-{ all haw/Curie temperatures f approximately to be withinthe scope of the teachings of the present f specification. Also, it isunderstood that the height of What 1S 1wned 133 the waveguide Section 12may be reduced to decrease 1. Aunidirectional microwave transmissiondevice comthe reluctance of the path of the magnetic flux and thusPnsmg: flf t a concomitant decrease in the Weight of the Pep (a) arectangular waveguide including a pair of opposite manem magnet 2 broadwalls and a pair of opposite narrow walls;

In Operation, electromagnafic energy is propagated by (b) a magnethaving a different pole piece adjacent Waveguide, including the section12 f a microwave each broad wall of said waveguide at a locationdisgenerator to load in the TELO mode at a group velocity, Vg taut froma first narrow wall of said waveguide beas indicated in the crosssectional plan Vie/W of the device tween the center of the surfaces ofthe broad walls of FIG. 1 shown in FIG. 4. In FIG. 4, dashed lines 32, asecond narrow Wall of said ide; 34 3 and 3 are representative of thefield configura (c) and an elongated slab of gyroresonant materialdistions of the magnetic fi ld of the pmpagated Wave. AS posedlongitudinally within said Waveguide substanggnemuy known these fieldconfigurations move through tially parallel to said broad walls thereof,said slab the Waveguide at the group velocity, Vg. Thus, the actualhaving a transverse width greater than" the width of magnetic fieldpresented to a point such as A in the fer- 130.16 pieces adjacent saidWaveguide? said Slabrite slab 20 is represented successively by vectorsa, b, emendlil'g transverse.ly across the Interior of 5 c, d, e and 3.There is a plane of circular polarization that w l f i toward sald finarrow wall from 3 P extends longitudinally of the waveguide where thevectors g dlsfliced i said first e Wall from the will rotate withuniform velocity; i.e., the energy is cirs gf 0' t 6 P0 6 pieces closestto Sam Second narrow y P Q Thls P121116 W111 move tlansvfifs'ely of 2. Aunidirectional microwave transmission device comthe waveguide as thefrequency of the energy varies. i

Inasmuch as the field configurations represented by (a) a rectangularwaveguide including a pair of opdashed lines 32, 34, 35, 38 areprogressing from the microposite broad walls and a pair of oppositenarrow walls and having substantially oppositely disposed longitudinalslots in said broad walls thereof, said slots being noncentrallydisposed between said narrow walls thereof;

(b) a magnet having a different pole piece adjacent each broad wall ofsaid waveguide and extending into the slots in said broad walls;

( c) and an elongated ferrite slab disposed longitudinally within saidwaveguide substantially parallel to said broad walls thereof, said slabextending transversely across the interior of said waveguide from saidslots toward the narrow wall farthest from said slots, the transversewidth of said slab being greater than the width of said pole piecesextending into said slots, said slab only partially overlaying the endsof said pole pieces disposed within said slots.

3. A unidirectional microwave transmission device comprising:

(a) a rectangular waveguide including a pair of 0pposite broad walls anda pair of opposite narrow walls;

(11) a magnet having a different pole piece adjacent each broad wall ofsaid waveguide at a location distant from a first narrow wall of saidwaveguide between the center of the surfaces of the broad walls and asecond narrow wall of said waveguide;

(c) and a pair of elongated ferrite slabs disposed longitudinally withinsaid waveguide substantially parallel to said broad walls thereof, adifferent one of said slabs being adjacent each broad wall of saidwaveguide, said slabs extending transversely across the interior of saidwaveguide toward said first narrow wall from a position displaced towardsaid first narrow wall from the edges of the pole pieces closest to saidsecond narrow wall.

4. A unidirectional microwave transmission device comprising:

(a) a rectangular waveguide including a pair of opposite broad walls anda pair of opposite narrow walls and having substantially oppositelydisposed longitudinal slots in said broad walls thereof, said slotsbeing noncentrally disposed between said narrow walls thereof;

(b) a magnet having a different pole piece adjacent each broad wall ofsaid waveguide and extending into the slots in said broad walls;

(c) and a pair of elongated slabs of gyroresonant material disposedlongitudinally within said waveguide substantially parallel to saidbroad wall-s thereof, a different one of said slabs being adjacent eachbroad wall of said waveguide, said slabs extending transversely acrossthe interior of said waveguide from said slots toward the narrow wallfarthest from said slots, the transverse width of said slabs beinggreater than the width of said pole pieces extending into said slots,said slabs only partially overlaying the ends of said pole piecesdisposed within said slots.

5. A unidirectional microwave transmission device comprising:

(a) a rectangular waveguide including a pair of opposite broad walls anda pair of opposite narrow walls and having substantially oppositelydisposed longitudinal slots in said broad walls thereof, said slotsbeing noncentrally disposed between said narrow walls of said waveguide;

(11) a magnet having a different pole piece adjacent each broad wall ofsaid waveguide and extending into the slots in said broad w-alls;

(c) and a pair of elongated ferrite slabs disposed 1ongitudinally withinsaid waveguide substantially parallel to said broad walls thereof, adifferent one of said slabs being adjacent each broad wall of saidwaveguide, said slabs extending transversely across the interior of saidWaveguide from said slots toward the narrow wall farthest from saidslots, the transverse width of said slabs being greater than the widthof said pole pieces extending into said slots, said slabs only partiallyoverlaying the ends of said pole pieces disposed in said slots.

References Cited in the file of this patent UNITED STATES PATENTS2,776,412 Sparling Ian. 1, 1957 2,806,972 Sensiper Sept. 17, 19572,849,684 Miller Aug. 26, 1958 OTHER REFERENCES Fox et al.: Bell SystemTechnical I ournal, J an. 1955, pages 42-53.

1. A UNIDIRECTIONAL MICROWAVE TRANSMISSION DEVICE COMPRISING: (A) ARECTANGULAR WAVERGUIDE INCLUDING A PAIR OF OPPOSITE BROAD WALLS AND APAIR OF OPPOSITE NARROW WALLS; (B) A MAGNET HAVING A DIFFERENT POLEPIECE ADJACENT EACH BROAD WALL OF SAID WAVEGUIDE AT A LOCATION DIS TANTFROM A FIRST NARROW WALL OF SAID WAVEGUIDE BETWEEN THE CENTER OF THESURFACES OF THE BROAD WALLS AND A SECOND NARROW WALL OF SAID WAVEGUIDE;